1. Field of the Invention
The present invention relates to a beam splitting unit for dividing a single laser beam into a plurality of laser beams, a beam-emission-angle compensating optical unit for correcting a beam emission angle, and a laser marking apparatus used for indoor and outdoor marking operations in house construction work.
2. Description of Related Art
In house building and particularly in the beginning phase of construction, marking operations are essential for producing level lines needed to set reliable baselines for positioning various building members when machining the members and for installing the building members. Level instruments and other tools are used at the building site to achieve level measurements. A plurality of marks is made on the walls of target structure, and marking lines are formed by connecting these marks to produce the baselines for construction.
These marking lines include various line beams, such as vertical lines drawn from the floor over the wall and to the ceiling, perpendicular (right angle) lines drawn on the. ceiling and made from two vertical lines, and horizontal lines drawn on the walls; ground mark dots formed on the floor; and the like.
Marking operations performed manually require at least two workers. Conventionally, marking operations have required much time and effort and have been inefficient. However, in order to overcome this problem, recently more efficient marking operations have been performed using a laser marking apparatus having a line beam irradiation function. Since one worker can easily perform marking operations using a laser marking apparatus, this apparatus is becoming an essential tool in construction work.
In order to improve the efficiency of marking operations using a laser marking apparatus, it is desirable to be able to irradiate a plurality of marking lines with a single laser marking apparatus. Hence, devices capable of irradiating two or more lines with a single apparatus are now being proposed.
Systems known in the art for irradiating a plurality of lines from a single laser marking apparatus include a system using a plurality of laser light sources and a system that obtains a plurality of lines by dividing a laser beam emitted from a single laser light source.
The former system is problematic in that the cost of the apparatus increases as more laser light sources are added.
On the other hand, the latter system uses a light-emitting optical system constructed of a plurality of half mirrors arranged serially in the laser emitting direction. An example of such a system is disclosed in Japanese patent application publication No. HEI-9-159451. In this system, however, the intensity of the light is cut in half after passing through the first half mirror and is reduced by halt again when passing through the second half mirror. Since the intensity of the light is gradually reduced when passing through each of the half mirrors in this way, the light intensity of the resulting divided beams is different from each other. Hence, a different brightness is obtained for each of the plurality of line beams. Further, a plurality of half mirrors must be arranged to divide the beam, thereby increasing the complexity of the optical system and, moreover, increasing the number of optical elements.
Accordingly, most conventional laser marking apparatuses capable of irradiating a plurality of line beams are equipped with a laser light source for each line beam generated. However, as described above, the cost of the apparatus rises as the number of light sources increases. As a result, an expensive apparatus is required to perform efficient marking operations.
The line directing precision of the laser marking apparatus becomes higher as the line beams irradiated by the laser marking apparatus approach ideal horizontal and vertical lines. In the conventional laser marking devices using the plurality of laser light sources, therefore, it is necessary to perform optical adjustments onto an optical system mounted in each laser light source in order to achieve good precision in directing lines. However, a lot of time and effort is required for assembling and adjusting these optical systems, thereby increasing the costs of the entire apparatus.
In the light-emitting optical system constructed of the plurality of half mirrors arranged serially in the laser emitting direction as disclosed in the Japanese patent application publication No. HEI-9-159451, it is necessary to finely adjust the angles at which the half mirrors are disposed in order to adjust the light-emission angle, at which light is emitted. This increases the complexity of the mechanism and the number of parts required therein. It is difficult to increase the precision for directing emitted light in this system disclosed in this publication, since this system has no particular mechanism for adjusting the angles of the half mirrors.